Surface energy measurements of coated titanium dioxide pigment

In this study surface energy measurements have been carried out on titanium dioxide pigments coated with different types of organic compounds. The organic coatings investigated were polymethylsiloxane and octyl triethoxy-silane. The level of coating applied was increased from 0.2 up to 1.5 wt%. Contact angles were measured using an advancing sessile drop method. To allow for the fact that measurements were made on pressed discs of particles rather than on a perfectly flat surface, a correction was applied to convert each measured contact angle to the true Young's contact angle. Surface energies were calculated from the corrected contact angles using the Owens and Wendt equation. From the values of surface energy it was possible to determine at what coating level the surface characteristics changed from hydrophilic to hydrophobic and hence when complete coverage had taken place. For both the siloxane and the silane coatings it was found that complete coating coverage occurred at an addition level of around 0.8 wt%. The surface energies of all the coated pigments were found to correlate well with their dispersion behaviour in liquid paraffin. (C) 2007 Elsevier B.V. All rights reserved.